This invention relates to the field of metal production and extraction, and in particular, to the extraction and production of zinc.
Zinc is commonly refined by electrolysis. In a typical process, a number of plate cathodes are each inserted into a separate electrolytic cell. The electrolytic cell contains a chemical solution which includes zinc. An electric field is applied to the cell and zinc is deposited on the cathode up to the height at which the cathode is submerged in the electrolytic cell. The zinc forms a sheet or count on the cathode. The upper edge of the zinc sheet is located at the xe2x80x9csolution linexe2x80x9d of the cathode, the line below which the cathode was submerged in the zinc solution. In order to harvest the zinc which has been deposited on the cathodes, it is necessary to separate the zinc sheets from the cathodes.
This removal is typically done by a zinc sheet stripping machine. Typically, the cathodes are removed from the cells, and are taken to the zinc stripping machine, which strips the zinc sheets from the cathodes. The cathodes are then returned to the cells to undergo the electrolytic process again, while the removed zinc sheets are gathered and stored.
This zinc stripping machine will, over time, physically damage the cathode and render it unfit for continued use in the electrolytic process. Since the cathodes are capable of being used over and over in the electrolytic process, it is most economical if the cathodes have a longer life. The more frequently the cathodes need to be replaced, the higher the cost to the producer. Thus, erosion, scratching and other damage to cathodes is a continuing problem for zinc producers.
Also, the electrolytic process operates by the application of a current between pairs of cathodes and anodes in the electrolytic cells. It is the electrical potential between the cathodes and anodes that causes the zinc to deposit on the cathodes. Such electroplating is most efficient when the cathodes and anodes are clean and free of surface impurities. For example, dirt on the surface of the cathode can affect the electrical currents preventing the plating of the zinc on the cathode in the dirty areas. Thus, zinc producers also have the problem of needing to keep the cathodes clean in an efficient manner.
Another problem for zinc producers and their employees is the significant amount of noise that is created in the harvesting of zinc from the cathodes. The cathodes themselves, the zinc sheets being removed from them, and the machinery used to remove the zinc sheets are all metallic. Thus, when these things come in repeated contact with one another, a great deal of noise can be generated.
Some zinc extraction plants have fixed installations for removing the zinc from the cathodes. Such fixed installations are often used in larger plants, where the cost of a larger fixed installation is justified. Also, typically, fixed installations are appropriate where there is a significant amount of space available for the zinc extraction process. In a fixed installation, the cathodes are typically fed into the input end of the fixed stripping installation, and then are moved through various parts of the machine, during which time the zinc sheets are stripped and the cathodes are carried to the output end of the fixed installation.
There are cases, however, where it is uneconomical to have a fixed zinc sheet removal installation. There are also cases where the zinc producer is confronted with floor space so limited as to preclude the use of a fixed installation. In such cases, it is preferable to have a mobile zinc stripping system which can be moved between various different groups of electrolytic cells and used to strip the cathodes adjacent to such electrolytic cells.
Canadian Patent No. 2,178,776 discloses a mobile automated cathode stripping system. The system includes a support frame for supporting a plurality of cathodes hanging vertically in parallel alignment with one another. The system further includes a stripping mechanism including a carriage framework mounted for linear movement along the support frame. The stripping mechanism includes a single pivotable stripping arm assembly, The assembly provides a pair of stripping knives, one for each side of each cathode, which wedge underneath the zinc sheet at the top corner of the sheet. The knives then move in an arc along the cathode under the zinc sheet, thus stripping the zinc sheet from the cathode and allowing it to fall by gravity. The zinc sheets are then moved into a receiving bin, and when the bin is full, the stack is moved to another location to be picked up by a lift truck and carried away. Jet spray heads are provided on the carriage which carries the stripping arm assembly. The purpose of the jet spray heads is to spray water at the zinc sheets and at the aluminum cathodes after they have been stripped, in an attempt to clean them. The jet spray heads are suspended above the cathodes, and spray water downward at a 45xc2x0 angle.
However, the system described in Canadian Patent No. 2,178,776 suffers from a number of defects. First, each side of the cathode is stripped by a single knife which traverses the entire vertical length of the cathodes. Such a stripping method erodes the aluminum cathodes unnecessarily, thus limiting their life.
Second, the water spray is not particularly effective, by itself, in cleaning the cathodes. This is particularly true in respect of any impurities which are stuck to the cathode. Such dirt may tend to stick despite the flow of water over them. Third, the device is awkward and difficult to use, because of the nature of the receiving bin for the stripped sheets.
U.S. Pat. No. 5,269,897 discloses an installation for removing the zinc deposited by electrolysis on aluminum plates. The installation includes a storage zone for coated cathodes, a scraping zone and a storage zone for zinc-free cathodes, with the cathodes being displaced consecutively from one zone to the next. The scraping zone includes a horizontally acting lateral piercer that separates the upper edge of the sheets of deposited zinc from the cathodes, and a vertically acting scraping device for removing all of the zinc sheets. The upper edge is separated by the lateral piercer being initially inserted under the zinc sheet. The heads of the piercer are then adjusted so that they no longer rest upon the cathode as the remainder of the upper edge is separated, thus reducing contact between the piercer and the cathode, and reducing damage to the cathode.
This patent, however, discloses a fixed installation where the cathodes are carried through the stripping device. Thus, the device disclosed in U.S. Pat. No. 5,269,897 is not appropriate for use where space is limited or where the cost of a fixed system is not justified.
Therefore, what is desired is a mobile zinc stripping machine that is effective in stripping zinc sheets from cathodes. The machine of the present invention will preferably operate so as to minimize damage to the cathodes during operation. It will also preferably be space efficient, be constructed so as to reduce the noise generated during the zinc stripping process, and be constructed so as to be able to effectively clean the cathodes after stripping.
Therefore, according to one aspect of the invention there is provided a device for stripping zinc sheets from cathodes, the device comprising:
a moveable base frame for moving the device along a floor;
a cathode support frame, coupled to the moveable base frame, the cathode support frame being sized, shaped and positioned to support the cathodes during stripping;
a stripping assembly for stripping the zinc sheets from the cathodes, the stripping assembly being movably coupled to the base frame and being moveable relative to the cathode support frame to permit the stripping assembly to strip each cathode supported in the cathode support frame;
at least one power source coupled to the base frame and operatively connected to the stripping assembly;
the stripping assembly including a lateral stripper, movable across the cathodes in the cathode support frame, for separating an upper edge of a zinc sheet from each of the cathodes, the lateral stripper being adapted to bias away from the cathode immediately upon entering between the zinc sheet and the cathode, and a scraping device, movable in a direction generally perpendicular to a direction of the lateral stripper, for completing removal of the sheet from each said cathode.
According to a further aspect of the invention, there is provided a device for stripping zinc sheets from cathodes, the device comprising:
a moveable base frame for moving the device along a floor;
a cathode support frame, coupled to the moveable base frame, the cathode support frame being sized, shaped and positioned to support the cathodes during stripping;
a stripping assembly for stripping the zinc sheets from the cathodes, the stripping assembly being movably coupled to the base frame and being moveable relative to the cathode support frame to permit the stripping assembly to strip each cathode supported in the cathode support frame;
a bottom-up stacker assembly coupled to the base frame;
a sheet carrier for transporting the zinc sheets to the stacker assembly, the sheet carrier being positioned so as to receive the zinc sheets when they are stripped, the stacker assembly being adapted to create a stack from the zinc sheets carried on the sheet carrier; and
at least one power source coupled to the base frame and operatively connected to the stripping assembly, to the sheet carrier and to the stacker assembly.
According to a further aspect of the invention, there is provided a device for stripping zinc sheets from cathodes, the device comprising:
a moveable base frame for moving the device along a floor;
a cathode support frame coupled to the base frame, the cathode support frame being sized, shaped and positioned to support the cathodes during stripping;
a stripping assembly for stripping the zinc sheets from the cathodes, the stripping assembly being movably coupled to the base frame and being moveable relative to the cathode support frame to permit the stripping assembly to strip each cathode supported in the cathode support frame;
at least one cathode cleaner, movably coupled to the base frame, the cathode cleaner being movable along the cathode support frame and along each said cathode so as to permit the cathode cleaner to clean each cathode supported on the cathode support frame; and
at least one power source coupled to the base frame and operatively connected to the stripping assembly.